runtime: use <stdbool.h>

<stdbool.h> has been available since C99. Use it rather than defining
our own boolean type and values.

Fixes https://gcc.gnu.org/PR114875

Change-Id: I9feff55465edb20cbcabee0846aea9d7ac73a97b
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/582275
Reviewed-by: Joedian Reid <joedian@google.com>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>
Reviewed-by: Than McIntosh <thanm@google.com>

libgo/runtime/runtime.h

diff --git a/libgo/runtime/runtime.h b/libgo/runtime/runtime.h
index 699770d..da31e11 100644
--- a/libgo/runtime/runtime.h
+++ b/libgo/runtime/runtime.h
@@ -7,6 +7,7 @@
 #include "go-assert.h"
 #include <complex.h>
 #include <signal.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -51,7 +52,6 @@
 
 /* Defined types.  */
 
-typedef	_Bool			bool;
 typedef	uint8			byte;
 typedef	struct	g		G;
 typedef	struct	mutex		Lock;
@@ -116,11 +116,6 @@
 
 enum
 {
-	true	= 1,
-	false	= 0,
-};
-enum
-{
 	PtrSize = sizeof(void*),
 };
 enum